MySQL Processes Not Dying?

I've got a odd problem. On one of my boxes (dual xeon 2.8ghz with 2gb ram) I host several medium forums. MySQL gets quite a lot of use with usually 5-15 connections in use at a time.

However, the processes seem to multiply without many dying off.

Example:
I restarted MySQL today at approx 10:12am EST.
The server starts with just a few processes.
Forums get used moderately during the day (being a weekend) - none use persistent connections.
Right now (8:30pm EST) there are 132 mysqld processes running (ps aux | grep mysqld | wc -l)

These processes are mostly using 0 cpu, but all are using some ram... and it all adds up.

Is there anyway to force mysql processes to die off after a certain amount of inactivity (like the apache min/maxservers)?

One idea... what would happen if a poorly written php script did NOT close its database connections at the end of execution... would the processes remain idle waiting for further instructions from that script (which of course would never come as it had finished execution)?